Membranes for use in reverse osmosis or nano-filtration are generally fabricated by interfacial polymerization of a monomer in a non-polar (e.g. organic) phase together with a monomer in a polar (e.g. aqueous) phase on a porous support membrane and are used, for example, in the purification of water. Such membranes are subject to fouling resulting in reduced flux as contaminants, for example from the water to be purified, build up on the surface of the membrane.
The general strategy for improving membrane performance has focused on i) addition of non-reactive solvent additives in organic or aqueous phases during interfacial polymerization, ii) post rinsing and treatment of the as made membrane after fabrication of barrier layer, and iii) addition of swelling agents after rinsing and prior to drying of the polymer membrane.
Various characterizations of membranes show that the structure of the polyamide barrier layer in thin-film composite (TFC) membranes is important to its performance and application. The polyamide layer of many TFC-membranes fabricated by interfacial polymerization of monomer units shows ridge-and-valley surface morphology and two distinct loose domains (carboxyl-rich and carboxyl-free) separated by a thin dense interlayer. Because the carboxyl-rich domain is on the top of the membrane, it introduces a negative charge on the membrane surface during normal operation conditions, which is a major factor that contributes to membrane fouling and flux decrease during operation.